I’ve built and sold lots of duelling trees. Some have lasted years of public range use. Qt400 plate lasts much longer than ar500. It wont hold up to rifle rounds, but it isn’t so hard that it breaks on the elbow.
Also, I’ve had the best luck with no springs or mechanical moving parts besides the swinging plates. 3/8” plate for strictly 9mm or 1/2” for 9mm and up. 5” rounds as well. 6” is too heavy.